Hi Islander,
no, I am not a control engineer. I used to do control structure architecture definition and HW and SW implementation for internal Service Control of big iron computers. 'RAS' - Reliability, Availability and Serviceability was my subject.
My limited knowledge about control is all self educated and related to using it to control gliders.
My interest is to make flying reproduceable so I can measure the influence of aerodynamic modifications. That is why I try to control airspeed with prime priority and rudder aileron correlation second.
I had the speed control working once (20 years ago) with an all analogue implementation. It was unstable and I could not reliably reproduce it after the plane crashed eventually.
Now that I am retiring I have picked up the old ideas and try to put them on a digital base.
I have found a number of good sensors, like the PCLA02X5G pressure transducer from Sensortechnics, the ADXL203 accellerometer and the ADXRS150 solid state gyro from Analog Devices. These are a far better starting point then my 'hot wire' anemometer I had buit myself and used 20 years ago.
I also have ambitious dreams about automatic finding of and centering in lifts. Or - 'intelligent control, which automatically finds best PID factors (hopefully before it crashes the model).
What are you doing?

Hi Klinke:
I am a graduate student, doing robotics and control. I am also an electronics/hardware engineer of a company in Taiwan. My profession began just two years ago, and I have been doing digital video recorders for these two years.
like you, I also made some experimental controllers, like heading hold gyros. But the result was limited to my skills at that time and could not be compared with commercial products. I hope this time I can do it much better than I could years ago.

I finally found some time to work on my idea to generate PCM with the soundcard. It seems to work; to looks good on the scope and when I feedback the generated signal to the soundcard input, the signal can be decoded again....

Now, the next thing I would like to try is to inject this signal to the RF part of the radio for transmission. I suppose I could find the place on the PCB where the digital signal is fed to the RF part.

But I am wondering how exactly the trainer connector works. When the PCM signal comes out of the trainer connector, is it also possible to inject a signal? My radio is a Robbe-Futaba FC-16

I also have a very old (20 years) Simprop radio. Here the RF part is completely separated, but I am not sure if the FM modulation of Simprop is compatible with Futaba (if I am not mistaken some radios modulate between f and f-d while others between f and f+d)

Hi Frederic:
The trainer port does not use the PCM mode, but the PPM mode. But I think anyway you can feed your signal into one of the pins of the TX module and use a standard PCM receive to verify your signal.
Good luck

Hi Frederic,
it may be worthwhile to omit the RF part for the time being and feed your signal into the DSC input of a Futaba PCM receiver.
Have fun...

What would be cool is a transmitter hardware platform that provides sticks, switches, a backlit LCD display a battery recess, and antenna.

The transmitter would run a small microkernel using open source software uploaded from a PC via a USB or serial port. The system would have a decent amount of RAM and a cheap but powerful processor.

The base operating system would expose a programmable interface that uploaded tools and utilities use to implement functionality. The owner could install or remove utilities as they see fit and completely customize their Tx.

This platform would use existing modules (for example, the Futaba synthesized module), thus obviating the need for building out the radio portion of the system (faster time to completion).

To verify that it works I used the pervious tools:
generatepcm | DecodePCM SI 1

I also made an application (signalout) that reads the pulse-widths from the console and generates the signal on the soundcard. Now I can do:

generatepcm | signalout

On the line-out of the soundcard I have a small circuit with a comparator to generate a clean signal of the correct amplitude and feed it to the trainer connector of the radio. The radio emits it as it where the signal from the student radio.

The receiver decodes the signal correctly and the servos are moving…

A problem is that the experiment board and the long cables pickup the RF signal from the radio. It now only works when I disconnect the antenna, but I believe this is not so good for the radio.

I have been searching the web for information about the trainer port. The information is scarce and contradictory.

The trainer port does not use the PCM mode, but the PPM mode

I have also read that somewhere. However I am quite positive, for my transmitter, there is PCM on the trainer port when configured for PCM. I suppose there are also different standards between the different Robbe/Futaba models. The FC-16 is a relatively old, relatively low-end model.

The trainer-connector on the pcb of my radio has 4 pins. Pin 1 is ground, Pin 2 is the battery tension (around 10V). Pin 3 and pin 4 are PCM (or PPM) signals, pin 4 a bit weaker than pin 3. From a description I found of the trainer-modules I figured out that the signal from the student radio is fed to pin 3 of the teacher radio (over a 1K resistor) when the switch is so that the student is in control. I suppose this information in incorrect and that the signal is fed to pin 4. When I connect pin 3 over a 3K3 resistor to ground, nothing happens, when I do this with pin 4, the receiver goes in FS. Pin 3 and 4 are interconnected by a 33K resistor on the radio PCB.

So, I think that pin 3 is the strong signal of the radio. Pin 4 is what is emitted. Due to the 33K resistor one can suppress the original signal and replace it. I am a bit surprised; does not look very clean to me…

Hi Vinnie,

Sure, that is possible.

My original idea was to add a processor that would decode the signal generated by the radio, add some functionality, generate PCM again for the radio to transmit. My FC-16 seems to be perfect for this setup as the trainer port provides power, the signal generated by the radio and allows to impose another signal for actual transmission…

Angelos is making HW that will replace the complete digital part of a radio; so he will also need ADC’s to reading the sticks and switches.

My approach has the advantage that is simpler and does not involve demolishing the radio. It has the disadvantage that the extra processor will probably be placed outside the radio, in the radio tray. In addition this setup will increase latency (not sure how important this is)

I am still not sure what I am going to do; execute my plan or go for Angelo’s approach.

Hi Angelos,

My point is that there is no way to feed PCM in which will be routed to the TX module.

You are still talking about the 9Z I presume. Correct?

I believe that for my radio things are different and simpler…

In some documentation I have read that the mixer settings of the teacher are used. This indeed would mean that a (PPM I presume) signal goes from student radio to the cpu of the teacher radio. I believe that for my radio things are much simpler and that it is the PCM or PPM signal from the student radio that is emitted directly by the teacher radio without involvement of the cpu.